Macro- and trace-element concentrations in leaves and roots of Phragmites australis in a volcanic lake in Southern Italy

Cr, Cu, Fe, K, Mg, Mn, N, Ni, Pb, S, V and Zn concentrations were determined during a whole seasonal cycle in leaves and in water and sediment roots of the aquatic macrophyte Phragmites australis (Cav.) Trin. ex Steudel from three sites in the Lake Averno (Naples, Italy), a volcanic lake contaminated by trace elements. At the beginning of the research, elemental analysis was also performed on lake sediments, that showed different trace-element concentrations depending on the sites. N, K, S and Mg contents in leaves and roots were of the same order of magnitude, whereas trace-element concentrations in roots were at least one order of magnitude higher than in leaves and increased with ageing, the maximum values being recorded in winter, at the end of the life cycle. N and K concentrations fluctuated during the seasonal cycle, with the highest values recorded during the phase of vegetative activity of the plants, whilst S and Mg contents showed no seasonal variation. Sediment roots, arising from the lower, chlorophyll-less parts of the culms and growing in the bottom sediments, were distinct from water roots, emerging from the green parts of the culms and floating in water, for their particularly prominent aerenchyma, a feature probably related to oxygen limitation. The two root types showed a different capacity to accumulate macro and trace elements. The results confirm P. australis as a particularly suitable plant for phytoremediation of polluted wetlands.